1. Field of the Invention
The invention relates to an element to be used in spinal column surgery or accident surgery with a shank and a holding element connected to it for connecting to a rod.
2. Description of Related Art
A bone screw with a shank and a holding element connected to it for connecting to a rod according to the preamble of claim 1 is known from EP 0 614 649. In this so-called polyaxial bone screw described the inner thread of the open legs of the holding element or receiving part and the outer thread of the inner screw have substantially a rounded thread.
From U.S. Pat. No. 5,005,562 and U.S. Pat. No. 6,074,391 in each case is known an element with a shank and a holding element connected to it for connecting to a rod, wherein the holding element comprises a recess having a U-shaped cross-section for receiving the rod with two legs open at one end and an inner thread on the open legs and a locking element with an outer thread which cooperates with the inner thread of the legs. The inner thread of the open legs of the holding element or receiving part and the outer thread of the inner screw are constructed with a saw-tooth pitch to avoid splaying of the legs by radially acting forces during screwing in.
An element with a shank and a holding element connected to it for connecting to a rod, wherein the holding element comprises a recess having a U-shaped cross-section for receiving the rod with two legs open at one end and an inner thread on the open legs and a locking element with an outer thread which cooperates with the inner thread of the legs is also known from WO 00/27 297. In this element the flanks of the inner thread facing away from the open ends of the legs formed by the U-shaped recess enclose a negative angle with a plane perpendicular to the central axis of the receiving part. This is also intended to prevent splaying of the legs.
In the above-described devices either a device encircling the holding element from outside is required to prevent splaying of the legs or the thread to be used is difficult to produce. This applies in particular to the thread known from WO 00/27 297 with the negative flank angle.
It is the object of the invention to provide an element with a shank and a holding element connected to it for connecting to a rod, which is easy to produce, compact in structure and easy to handle.